The invention relates in the broadest sense to a method for producing blank-pressed glass bodies for optical equipment by preshaping technology, in which a single molten glass gob is delivered to a levitation parison mold, and the glass gob, without touching the parison mold surface, is preformed into a parison, which, after a defined length of time has elapsed, is transferred to a separate press mold and is pressed therein into its final form by means of a press tool. To that end, the parison mold is moved across the press mold for the transfer of the glass gob and is stopped in a transfer position and then pivoted downward, away from the glass gob. The actual invention relates to a device for blank pressing optical glass bodies, which comprises two rotary indexing tables, of which one has circularly disposed parison molds for making the parisons from molten glass gobs, each of which have extremely tiny openings in their lower region for introducing an air cushion, and the other has circularly disposed press molds for pressing the parisons after transfer from the parison molds.
It is known to produce glass bodies for the production of optical equipment, such as lenses, prisms, etc. in highly polished forms, by repressing re-warmed, blank (fire-polished) glass rods. The re-pressing is necessary to attain the final precise surface optical quality for the glass bodies. In producing some glass bodies, such as aspherical lenses for automobile headlights, however, the re-pressing operation alone is insufficient. Milling, grinding and polishing operations are necessary in addition. In producing blank-pressed condenser lenses, for instance, only the aspherical surface is blank-pressed, while the plane face opposite the blank face is milled, ground and polished by mechanical operations.
The manual re-pressing and the additional method steps that may be necessary dictate a time-consuming, expensive mode of production. Since there is a very great need for blank-pressed glass bodies, in particular lenses for automobile headlights, the demand for automatic production directly from the molten phase of the glass, that is, after an in-line blank pressing process, arises.
This kind of automatic production is possible by means of the preshaping technology defined at the outset, which is known for instance from German Patent Disclosure DE-A 24 10 923. The transfer of the glass gob from a parison mold is affected according to this reference by placing the glass gob on a kind of chute along which the parison is guided in the hot state to a pressing mold. This causes surface defects and changes of shape, which are currently no longer tolerable. The change in shape furthermore leads in the final analysis to an uneven temperature distribution. This too has an adverse effect on shaping in the ensuing pressing operation.
In Japanese Patent Disclosure JP-A 11-157 849, a method of the above-described kind has been disclosed. In it, the transfer of the glass gob from a parison mold is accomplished by opening the parison mold and causing the glass gob to drop into a press mold in free fall. This avoids surface defects and changes of shape. However, there is no way to tell how the interaction of the parison mold and the press mold proceeds.
Further methods in this field are known from Japanese Patent Disclosure JP-A 06 206 730 and U.S. Pat. No. 5,762,673.